1. Field of the Invention
The present invention generally relates to surfactant blends and their use as adjuvants in applications for dispersing, wetting and spreading pesticides. More particularly, the present invention relates to blends of an organosilicone compound and a polyalkyleneoxide copolymer for use in such applications.
2. Prior Art
Nonionic surfactants are commonly used in forestry and horticulture as agricultural adjuvants to improve the efficacy of pesticides such as micronutrients, biologicals, herbicides, fungicides and growth regulators. Surfactants play several roles in this application, including dispersings, wetting, spreading and emulsifying, either as part of the formulated product or as a tank side post-add.
Nonionic surfactants are well known for their ability to reduce the surface tension of aqueous solutions. This reduction in surface tension is important for the spreading of solutions on difficult to wet surfaces, such as a waxy leaf cuticle. Surfactants aid in the uptake of active ingredients into the plant tissue through permeation of the cuticle, through defects in the surface, and in some special cases, through flooding of the leaf stomata. Although conventional nonionic surfactants enhance the wetting of spray formulations they do not provide total wetting on hydrophobic leaf surfaces. This can result in poor uptake of active ingredients and a low degree of rainfast efficacy.
Recently, organosilicone compounds have drawn attention as agricultural adjuvants because of their unique wetting properties. Zabkiewicz, J. A. Gaskin, R. E. and Balneaves, J. M., 1985. Effect of Additives on Foliar Wetting and Uptake of Glyphosate into Gorse. pp. 127-134. In: Application and Biology (BCPC Monograph No. 28) ED: Southcombe, E.S.E. BCPC, 2a Kidderminester Rd, Croydon, CRO 2UE, U.K. lSBN 0-9014368-7-9. These surfactants give surface tension values significantly lower than conventional nonionic surfactants (21 dynes/cm vs 30 dynes/cm). It has been demonstrated by Zabkiewicz et al. some select organosilicone surfactants provide a significant increase in the foliar uptake of herbicide into gorse, when compared to conventional wetting agents.
Also, these spreading of aqueous solutions of the organosilicone compounds give total wetting (as measured by contact angles) on leaf surfaces, while conventional organics give significantly higher contact angles.
The interaction for a variety of surfactant pairs is well documented in the open literature. D. N. Rubingh, 1982, Mechanism of Detergency in Systems Containing Cationic and Nonionic Surfactants, Ind. Eng. Chem. Prod. Res. Dev., 21, 176-182 demonstrated that a reduction in the critical micelle concentration as well as a reduction in surface tension is observed for a variety of surfactant pairs. Rosen, Molecular Interaction and Synergism in Binary Mixtures of Surfactants, ACS Symp. Ser., Vol. 311, page 144 (1986) further showed that interactions between nonionic organic and ionic organic surfactant pairs demonstrate surface tensions lower than would be expected for mixtures of the two organic surfactants (non-ideal behavior). However, the degree of interaction for nonionic/nonionic surfactant pairs was limited. Generally, Rosen supports the belief that these surfactant pairs display ideal solution behavior.
The prior art described by Rosen, and Rubingh deal with interactions between organic surfactant pairs. The interactions for nonionic/nonionic surfactant pairs is limited while the present invention demonstrates significant and unexpected interaction between a nonionic polyalkyleneoxide copolymer and a nonionic organosilicone compound.
U.S. Pat. No. 3,562,786 (Bailey) described mixtures of nonionic organosilicone compounds with conventional organic nonionic and ionic surfactants. The organosilicone compound is claimed to be useful in lowering the aqueous surface tension of organic surfactant solutions.
The nonionic surfactants described by Bailey deal primarily with nonylphenol or alcohol ethoxylates. These materials, when used as a cosurfactant for the organosilicone compounds described in this invention, interfere with the spreading characteristics of the organosilicone compounds. The present invention describes a specific synergistic surfactant composition, where the organic cosurfactant does not interfere with wetting or spreading of the organosilicone compound.